﻿FOURTH 
  REPORT 
  OF 
  THE 
  DIRECTOR 
  I907 
  1 
  53 
  

  

  faunas 
  adapted 
  themselves 
  to 
  life 
  in 
  shallow 
  waters 
  did 
  the 
  necessity 
  

   for 
  shell 
  protection 
  arise 
  for 
  with 
  this 
  change 
  from 
  a 
  free-swimming 
  

   to 
  a 
  creeping 
  or 
  stationary 
  littoral 
  habit 
  came 
  the 
  lessened 
  capacity 
  

   for 
  escape 
  by 
  locomotion. 
  As 
  Lang 
  has 
  said, 
  the 
  coast 
  is 
  full 
  of 
  

   dangers; 
  the 
  waves 
  beat 
  violently 
  against 
  it, 
  the 
  regularly 
  re- 
  

   turning 
  tide 
  keeps 
  the 
  waters 
  ever 
  moving. 
  From 
  these 
  attacks 
  of 
  

   nature's 
  blind 
  forces 
  the 
  creatures 
  must 
  protect 
  themselves. 
  Some, 
  

   in 
  times 
  of 
  stress, 
  seek 
  deep 
  water, 
  some 
  scuttle 
  into 
  protected 
  

   spots 
  or 
  bury 
  themselves 
  in 
  the 
  sand, 
  and 
  others 
  catch 
  hold 
  of 
  

   stable 
  bodies, 
  attaching 
  themselves 
  by 
  suction 
  or 
  fixation. 
  But 
  all 
  

   these 
  resorts 
  are 
  inefficient 
  without 
  the 
  addition 
  of 
  shell 
  protection 
  ; 
  

   that 
  once 
  achieved, 
  the 
  animals 
  may 
  rejoice 
  and 
  flourish 
  in 
  the 
  

   play 
  of 
  the 
  waves 
  which 
  brings 
  them 
  nourishment 
  with 
  decreased 
  

   exertion 
  on 
  their 
  part. 
  The 
  primary 
  step 
  toward 
  a 
  degeneration 
  

   which 
  in 
  the 
  lapse 
  of 
  ages 
  has 
  led 
  to 
  the 
  dependent 
  life 
  conditions 
  

   of 
  today 
  would 
  seem 
  with 
  reason 
  to 
  lie 
  in 
  the 
  forced 
  reduction 
  of 
  

   this 
  locomotive 
  power 
  and 
  adaptation 
  to 
  a 
  sedentary 
  condition 
  

   resulting 
  in 
  the 
  necessity 
  for 
  the 
  formation 
  of 
  a 
  protective 
  shell. 
  

  

  ILLUSTRATIONS 
  OF 
  PALEOZOIC 
  SYMBIOTIC 
  ASSOCIA- 
  

   TIONS 
  

  

  The 
  instances 
  here 
  given 
  are 
  some 
  of 
  the 
  more 
  instructive 
  occur- 
  

   rences 
  of 
  this 
  sort 
  that 
  have 
  come 
  under 
  my 
  notice. 
  They 
  are 
  not 
  

   in 
  all 
  cases 
  common 
  though 
  they 
  exemplify 
  consociations 
  which 
  are 
  

   familiar 
  in 
  like 
  groups 
  of 
  the 
  living 
  world. 
  The 
  record 
  of 
  their 
  

   number 
  will 
  doubtless 
  be 
  much 
  increased 
  as 
  such 
  objects 
  come 
  under 
  

   closer 
  observation. 
  The 
  collection 
  of 
  such 
  data 
  from 
  the 
  early 
  

   periods 
  of 
  the 
  world's 
  life 
  is 
  not 
  likely 
  to 
  be 
  carried 
  too 
  far 
  for 
  it 
  is 
  

   here, 
  rather 
  than 
  in 
  a 
  profuser 
  and 
  much 
  more 
  complicated 
  later 
  

   development, 
  that 
  the 
  factors 
  of 
  symbiosis 
  are 
  the 
  more 
  easily 
  

   legible. 
  

  

  Worms 
  and 
  Corals 
  

   The 
  coexistence 
  of 
  the 
  tubicolous 
  worms 
  with 
  the 
  corals 
  is 
  one 
  of 
  

   the 
  commonest 
  phenomena 
  of 
  present 
  seas. 
  It 
  became 
  established 
  

   at 
  a 
  very 
  early 
  stage 
  in 
  the 
  earth's 
  history 
  and 
  in 
  the 
  Devonic 
  coral 
  

   reefs 
  the 
  habitude 
  had 
  already 
  become 
  widespread 
  and 
  varied. 
  It 
  

   was 
  palpably 
  less 
  frequent 
  in 
  Siluric 
  times 
  r 
  at 
  least 
  our 
  material 
  

   would 
  so 
  indicate, 
  and 
  when 
  it 
  does 
  present 
  itself, 
  the 
  expression 
  

   is 
  quite 
  simple. 
  In 
  most 
  cases 
  it 
  is 
  an 
  elementary 
  expression 
  of 
  

   commensalism. 
  Worm 
  and 
  coral 
  may 
  start 
  to 
  grow 
  together 
  di- 
  

  

  